Total Party Kill. When the opponents of the player characters end up killing all the player characters. Often unexpected, and sometimes blamed on poor understanding by the GM of difficulty level of the opponents.
A new game system that closely emulates an older edition of a game system that is out of print in order to compatible with anything produced for the older system. Often, but not always, derived from Open Gaming materials under the Open Gaming License (OGL) or similar public copyright licenses.
Labyrinth Lord (LL1, LL2, LL3) and Old School Essentials (OSE1, OSE2) are retro-clones of B/X D&D (B1, B2, X1, X2). Swords & Wizardry Complete (S&W1, S&W2) is a retro-clone of Original D&D plus some additional material from The Strategic Review and Dragon magazines. OSRIC is a retro-clone of Advanced Dungeons & Dragons.
A new game system that is inspired by an older edition of a game system, but which uses somewhat different mechanics.